1. University Laboratory Animal Resources, University of Pennsylvania, Philadelphia, Pennsylvania
2. Gene Therapy Program, Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
3. Cornell University, New York State College of Veterinary Medicine, Ithaca, New York
4. University Laboratory Animal Resources, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Pathobiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania;, Email: marx@upenn.edu